1. Field of Invention
The present invention relates to a pixel circuit, and more particularly relates to an AMOLED pixel circuit including a capacitor for sustaining light emission of the OLED.
2. Description of Related Art
FIG. 1 shows an organic light emitting diode pixel circuit of prior art. The pixel circuit has a light emitting diode 180, a driving transistor 140, a, and a capacitor 130, and a switch unit (transistor 160). The driving transistor 140 has a first source/drain 141 coupled to a first end 181 of the light emitting diode 180. The capacitor 130 is coupled between the gate and the first source/drain 141 of the first driving transistor 140. When a scan signal is asserted, the transistor 160 couples the gate and the second source/drain 142 of the first driving transistor 140 together. When the scan signal is de-asserted, the transistor 160 decouples the gate from the second source/drain 142 of the first driving transistor 140.
The pixel circuit also has a scan switch 110 coupled to a data line 120 and is controlled by the scan signal. The second source/drain 142 of the first driving transistor 140 is coupled to a power source terminal 190.
The drawback of the conventional pixel circuit is that it spends a relatively long time for the capacitor 130 to be charged to a required level, especially for low gray scale level images. Therefore, a pixel circuit with high data writing speed is needed.